1. Field of the Invention
The invention relates to a prefabricated steel/ concrete composite beam arranged to act together with concrete as a load-bearing composite structure for various slab assemblies.
2. Discussion of the Related Art
The invention concerns a beam utilizing a steel beam/concrete composite structure. Such beams are today well-known in element structures. One example of the prior art is the solution described in Finnish Patent Application 882 186. The composite structure makes the steel beam lighter, and the beam can be used over longer span lengths than what has been possible previously. The steel beam according to Finnish Patent Application 882 186 reduces the amount of welding work as the beam is made of profile sections preformed by hot rolling. However, the beam structure according to Finnish Patent Application 882 186 is complicated to manufacture as connecting pieces by means of which the composite structure is achieved increase the amount of welding. The handling of a plurality of small pieces as such complicates the manufacture of the beam.
Another example of the prior art is the solution disclosed in Finnish Published Specification 85 745, which eliminates the drawbacks of the solution disclosed in Finnish Patent Application 882 186. A drawback of Finnish Patent Application 85 745, however, is that if the solution is applied without a lower flange or without a fire-proof lower flange, the strength of the structure will not be the best possible in the case of fire. A similar situation occurs when the strength of the lower flange deteriorates significantly during a fire. The concrete contained in the beam thereby tends to be squeezed out, and the structure will not operate in a desired manner.
An object and summary provide a prefabricated steel/concrete composite beam which eliminates the drawbacks of the prior art. This is achieved by means of a beam according to the invention which is characterized in that at least one plate-like member is disposed substantially vertically in the space defined between the web portions and the horizontal top portion, the plate-like member being provided with openings positioned with mutual spacings successively in the longitudinal direction of the beam, and being attached at the upper edge to the lower surface of the horizontal top portion.
An advantage of the prefabricated beam according to the invention is mainly that the extrusion of concrete out of the beam is prevented e.g. when the lower flange has lost its ability to operate at high temperatures. Another advantage is that the invention is simple and therefore advantageous to take into use. Still another advantage of the invention is its versatility as it can be used both with prestressed beams and with beams that have not been prestressed.